Continuing our coverage of the 2014 AIA COTE Top Ten green projects, this article is part of a series of 10 pieces that examine a specific, defining design challenge or innovation of each of this year's winners.
Every afternoon, when an astronomical clock calculates that the sun is broiling the southwest-facing offices of the David and Lucile Packard Foundation Headquarters in Los Altos, Calif., exterior blinds automatically descend to shield the windows on that elevation. By early evening, these automated aluminum blinds are back up, ready to admit the soft morning light that makes it all but unnecessary for employees to reach for a light switch.
The automated blinds are just one of the ways that this net-zero-energy (NZE) building, designed by San Francisco–based EHDD, neutralizes its energy consumption through a combination of active and passive strategies. In its first year of operation, the two-story, 49,000-square-foot building actually registered net positive with a net energy use intensity (EUI) of -4 kBtu per square foot per year.
The offices are distributed in two linear wings separated by a courtyard, putting all occupants within easy reach of operable windows and the shared outdoor “living room.” Although daylight permeates the interior, glare is checked by roof overhangs, balconies, trees, and interior blinds—which are user-controlled, but rise automatically each night. When artificial light is needed, thrifty, self-dimming LED fixtures emit minimal heat, reducing the need for energy-intensive ventilation.
Every possible source of heat gain, heat loss, and electricity consumption in the Packard building was re-evaluated to reduce energy loads. For example, EHDD specified triple-element windows (R-7.7) to prevent thermal loss and infiltration. They cut electrical plug loads by more than 50 percent by specifying only the very top-rated Energy Star equipment. That is why, although the 285-kW photovoltaic array covering the roof sounds formidable, it would be far too modest to power a more conventionally designed building of this size. The investments in windows and plug load reduction alone saved an estimated $700,000 worth of PV panels (the as-built array cost around $1.6 million).
For the cooling system, EHDD devised a way to chill water naturally. Exploiting the Bay Area’s reliably large temperature swings between day and night, compressor-free cooling towers chill water overnight. The chilled water is stored underground in 50,000-gallon tanks, then, in the heat of the day, pumped through the building’s radiant cooling panels, called “lightshelves,” and suspended diffuser beams. The lightshelves, mounted near the windows, double as anti-glare devices, “like the brim of a hat sticking out into the room,” explains Brad Jacobson, AIA, senior associate and sustainability leader at EHDD, and project manager for the Packard project.
The radiant cooling system was among the technologies that outperformed expectations during the first year, leading to less energy expended on pump and fan use. On the other hand, the all-electric heating system, which delivers heat through the ventilation air supply, used more energy than predicted, due in part to thermal bridging and infiltration. Half of the air-source heat pumps failed, requiring diagnostics and repair. The post-occupancy team was able to troubleshoot the problems by analyzing real-time data from the sensor network that monitors every point in the system.
The lessons learned can inform future NZE projects in this climate. “We should design more to reduce heating needs and worry less about cooling,” suggests Jacobson. The Packard project also exemplifies how the client and architect must work together to envision post-occupancy operation, monitoring, and adjustment. Beyond the impressive energy metrics, however, occupants have reported an increased sense of community and workplace satisfaction due, in part, to the courtyard. Perhaps, as EHDD suggests, “a more sustainable life is simply a better life.”